The present patent application for industrial invention relates to a single-blade rotor designed to be used as main rotor in helicopters and other types of rotorcraft. The rotor supports the helicopter during hovering and translated flight and, by means of its controls, allows execution of the manoeuvres typical of this type of vehicle.
To this end, helicopters are usually equipped with vertical axis rotors provided with two or more identical blades joined by hinges or similar means to a central propeller hub, which is in turn fixed to the upper end of a vertical mast driven by a system for the transmission of the rotary motion connected to one or more engines.
When maintained in rotation at the appropriate speed, the blades support the helicopter because of the upward lift produced as a consequence of the relative air speed with respect to the aerodynamically profiled blades. Moreover, the blades are subject to the weight force and, due to rotation, to the centrifugal force. The balance of all these forces and their moments with respect to the joints of the blades to the rotor hub and the mast, to which the weight of the rotorcraft is applied, determines the geometrical position of the blades, which, with respect to the plane orthogonal to the rotation axis, are directed upwards with a normally small coning angle. The entity of the total lift is adjusted by the pilot through the collective control lever that acts on the blade pitch by means of rods, levers, and rotating mechanisms connected with suitable pitch horns located on the hub of each blade, coupled in a rotary way to the rotor hub, with rotation axis sensibly parallel to its own longitudinal axis.
The control mechanisms allow the pilot to change the pitch of each blade with the cyclic control lever, with respect to the average value determined by the collective control, in order to create pitch differences symmetrical to this average value, in positions diametrically opposed to the rotational axis, inducing the rotor disk to tilt, thus causing the helicopter to move in the corresponding direction of tilting.
Rotors are usually manufactured according to multiple solutions, all of which, in order to guarantee correct operation, require the blades to be identical in terms of entity and mass distribution and as similar as possible in terms of shape and aerodynamic behaviour, while the joints at the rotor head and the kinematic chain that controls their pitch must have the same characteristics for all the blades of the rotor. Therefore, in order to maintain acceptable performance, such rotors require frequent maintenance works of blades tracking and balance, involving complicated procedures and methods and using special equipment.
In such multi-blade rotors, the lifting surface is divided between the blades of the rotor. With the same diameter and solidity, in a multiblade rotor each blade has a shorter mean chord which, for a given rotor tip, results in a lower value of the ratio between the product of the speed multiplied by the chord and the kinematic viscosity of the air (Reynolds Number). Since this lower value results in an increased blade drag coefficient for a given lift, it is therefore convenient to reduce the number of blades.
Moreover, it must be stressed that the rotation of each lifting blade produces a wake that can disturb the following blade, especially during hovering or low speed flight, with negative effects on its performance. The time interval between the passage of one blade in a disk area and the following as the number of rotor blades decreases, under given conditions, thus reducing the perturbation of the air in which the rotor operates.
In view of the above considerations, whenever possible, the adoption of a reduced number of blades can give aerodynamic advantages over similar rotors with a higher number of blades. Moreover, the reduction in the number of blades decreases the number of components and moving parts, leading to the simple bi-blade rotor with suspended hub connected to the mast with a horizontal hinge normal to the rotation axis.
Experiments have also been carried out with single-blade rotors in which the blade is balanced by a counterweight, but the difficulties in obtaining an acceptable balance between the forces and moments acting on such rotors under various operating conditions have not allowed the application and diffusion of such solutions.
The main purpose of the present invention is to overcome the inconveniences found in multi-blade and single-blade helicopters of known type, by means of a main rotor system for helicopters consisting of a single blade with central hub, a counterweight and balancing devices, having high flexibility and adaptability and characterised by easy construction, safe use and efficient operation.
The second purpose of the present invention is to create a single-blade rotor system, with working mechanism, in which the balance of the forces and moments acting on its parts is obtained by means of the reciprocal positions assumed by these parts as the coning angle of the single blade varies. The mechanisms controlling rotor balancing may be kinematic systems of known type, or other electromechanical or hydraulic devices. In any case, the horizontal component of the lift of the single blade is balanced by an identical opposed misbalance of centrifugal inertial forces, obtained by moving the rotor centre of mass relative to its rotation axis.
The third purpose of the present invention is to devise a rotor system, with control mechanisms, which does not require blades-tracking to ensure correct operation.
Last, but not least, another aim of the present invention is to design a mechanism capable of creating and maintaining a stable balance between the elements of the single-blade rotor during operation.
These and other aims, which will be highlighted in the description below, can all be achieved by the present invention.